1. Field of the Invention
The present invention generally relates to an apparatus for controlling the power output of a throttle controlled engine given a malfunction in the throttle control. More particularly, an engine controller regulates engine speed and power by modulation the supply of fuel or the selection of transmission gearing to maintain engine power at a level preceding the malfunction.
2. Description of the Related Art
Generally, a vehicles engine speed or velocity is in large part determined by the drivers manipulation of an acceleration pedal or similar means. Such means are usually mechanically coupled via a wire or the like to a throttle valve provided in the air-intake passage of the engine. The amount of the movement (angle) of this valve is specifically controlled in accordance with the mount of the pedal manipulation. The action of the valve controls the amount of air led into the engine via the air-intake passage.
Recently, throttle valves have been introduced which, are not mechanically couple to a pedal. One example of such a valve is used in an engine controller disclosed in Japanese Unexamined Patent Publication No. 62-35039.
A throttle controller is shown in FIG. 25 that uses a potentiometer 72 to detect the amount by which the driver manipulates the accelerator pedal 71. Based on the detected manipulation amount, a first control circuit 74 determines a target angle for a throttle valve 73. With the target angle as a control value, a step motor 75, controlled by the control circuit 74, manipulates the angle of the valve 73 to control the engine power.
Should there be a malfunction with either the throttle control system or the step motor, there should be some means for controlling the throttle. Conventional controllers, such as in Japanese Unexamined Publication No. 62-35039, use the following structure as a backup system.
The rotational speed of the engine ("engine speed") is detected by a crank angle sensor 76 which detects the rotational angle of the crankshaft. Based on the detected engine speed, a second control circuit 77 determines a target amount of fuel to be injected into the engine, and assigns a value to that amount. Based on the target value, the second control circuit 77 controls a fuel injector 78 which delivers the target amount of fuel, determined by control circuit 77, to the engine. By using throttle sensor 79, a signal based on the angle of the throttle valve 73 is supplied to the first control circuit 74 which determines if the throttle control system has failed. In this example, if the throttle angle is zero when the valve 73 should be fully open, the throttle control system is considered as having malfunctioned.
Depending on the engine speed detected by the crank angle sensor 76, the first control circuit 74 determines whether the electric sensor system or sensor 76 has failed. When the first control circuit 74 determines that a failure has occurred in throttle control system, fuel injection is intermittently interrupted or cut (fuel cut) by the injector 78. This effectively controls the fuel supply to the engine so that the engine speed becomes equal to or lower than a preset reference value, despite the current engine speed. Excessive engine speeds can thus be avoided in circumstances where the throttle control system has failed. When the difference between the value of the engine speed upon occurrence of the failure and the reference value is relatively large, the engine is rapidly decelerated at the instant when the failure is detected. The engine in that case undergoes a noticeable and sometimes rapid deceleration.
Upon the detection of a failure in either the throttle control system or the electric sensor system, an uninterrupted fuel cutting procedure is instituted irrespective of the particular engine speed or velocity at the time of fuel cutting.
Depending on the particular engine speed or velocity at the time of fuel cutting, the engine deceleration may degrade the optimum performance and drivability characteristics of the vehicle.